Protectors for electric circuits



Aug. 5, 1969 A. J. r-'lsTER PROTECTORS FOR ELECTRIC CIRCUITS Filed Sept. 25, 1967 United States Patent O 3,460,086 PROTECTURS FOR ELECTRIC CIRCUITS Aloysius J. Fister, St. Louis, Mo., assignor to McGraw- Edison Company, Elgin, Ill., a corporation of Delaware Filed Sept. 25, 1967, Ser. No. 670,231 Int. Cl. H01h 85/14, 85/02 U.S. Cl. 337-202 12 Claims ABSTRACT OF THE DISCLOSURE A small amperage, relatively-high voltage fuse is provided with a short casing which is devoid of arc-extinguishing filler material in which the position of the fusible element of the fuse is -xed within the casing and if barriers of insulation are disposed immediately adjacent the inner faces of the terminals at the opposite ends of the casings to prevent arc plasma from extending between those inner faces.

This invention relates to improvements in protectors for electric circuits. More particularly, this invention relates to improvements in electric fuses which are used to protect relatively-high voltage circuits.

It is, therefore, an object of the present invention to provide an improved electric fuse Iwhich can be used to protect relatively-high voltage circuits.

Where fuses are used to protect relatively-high voltage circuits and are provided with short casings, it is customary to fill those casings with arc-extinguishing filler material. However, where the amperages of such fuses are small, the cross-sections of the fusible elements of those fuses are so small that it is difficult to obtain uniform transference of heat from those fusible elements to the surrounding arc-extinguishing filler material. For example, if the arc-extinguishing filler material is a granular material such as quartz sand, there will be minute voids between the grains of that arc-extinguishing iiller material and the fusible elements, and those voids will have a lower heat-transferring capability than will those grains. On the other hand, if the arc-extinguishing ller material is an amorphous material, such as calcium sulfate, the forces which must be used to compact that arc-extinguishing ller material within the casings of the electric fuses can displace the fusible elements from their intended positions within those casings, and can even break thosefusible elements. Furthermore, even if the amorphous arc-extinguishing material could be compacted around the fusible element without breaking that fusible element, that arc-extinguishing ller material would tend to develop cracks or voids as the electric fuse was handled; and those cracks or voids would have a lower heattransferring capability than would that arc-extinguishing iiller material. Consequently, it would be desirable to provide an electric fuse which could be used to protect relatively high-voltage circuits but which could be provided with a short casing that was devoid of arc-extinguishing ller material. The present invention provides such an electric fuse; and it is, therefore, an object of the present invention to provide an electric fuse which can be used to protect relativelyhigh voltage circuits and which can be provided with a short casing that is devoid of arc-extinguishing ller material.

The present invention makes it possible to provide an electric fuse which can be used to protect relatively-high voltage circuits and which has a short casing that is devoid of arc-extinguishing -ller material by xing the position of the fusible element of that fuse within that casing and by disposing imperforate barriers of insulation adjacent the inner faces of the terminals at the ends of that casing. The fixing of the position of the 3,460,086 Patented Aug. 5, 1969 ICC fusible element within that casing provides a determinable rate at which heat will radiate from that fusible element to the walls of that casing, and thus enables the electric fuse to have a predictable and uniform rating. The positioning of the imperforate barriers of insulation adjacent the inner faces of the terminals of the electric fuse will keep arc plasma from extending between those terminals when the fusible element fuses. The overall result is that the electric fuse provided by the present invention has a predictable uniform rating and can safely interrupt a relativelyahigh voltage circuit. It is, therefore, an object of the present invention to provide an electric fuse wherein the position of the fusible element within the casing is fixed and wherein irnperforate barriers of insulation are disposed adjacent the inner faces of the terminals at the ends of that casing.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description, several preferred embodiments of the present invention are shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing, FIG. 1 is a longitudinal section through one preferred embodiment of electric fuse that is made in accordance with the principles and teachings of the present invention,

FIG. 2 is an exploded view of the electric fuse shown in FIG. 1,

FIG. 3 is a longitudinal section through another preferred embodiment of electric fuse that is -made in accordance with the principles and teachings of the present invention,

FIG. 4 is a longitudinal section through one end of a third preferred embodiment of electric fuse that is made in accordance with the principles and teachings of the present invention, and

FIG. 5 is a longitudinal section through one end of a fourth preferred embodiment of electric fuse that is made in accordance with the principles and teachings of the present invention.

Referring to the drawing in detail, the numeral 20 denotes the casing of one preferred embodiment of electric fuse that is made in accordance with the principles and teachings of the present invention. That casing is made of insulating material; and it is tubular in form. An annular groove 22 is formed in the exterior of that casing adjacent the left-hand end of that casing; and a similar annular groove 24 is for-med in the exterior of that casing adjacent the right-hand end of that casing. The annular grooves 22 and 24 are made shallow so they will not unduly weaken the casing 20.

The numeral 26 denotes a cup-shaped washer of generally frusto-conical form; and that cup-shaped washer is formed so the frusto-conical portion thereof can be pressed into the left-hand end of the casing 20, as that casing is viewed in FIG. l. An annular flange projects outwardly from the large-diameter end of the frusto-conical portion of the washer 26; and that flange is dimensioned to abut the left-hand end of that casing. A small opening 28 is formed in the center of the closed end of the frustoconical portion of the cup-shaped washer 26. The numeral 30 denotes a cup-shaped barrier of frusto-conical form; and that barrier is dimensioned to telescope within the recess in the frusto-conical portion of the cup-shaped washer 26.

The numeral 32 denotes a second cup-Shaped washer which can be identical to the cup-shaped washer 26; and

that second washer is dimensioned to be pressed within the right-hand end of the casing 20. A small opening 34 is formed in the center of the closed end of the frustoconical portion of that second washer. The numeral 36 denotes a second cup-shaped barrier which can be identical to the cup-shaped barrier 30; and that second cup-shaped barrier is dimensioned to telescope within the recess in the frusto-conical portion of the second washer 32.

The cup-shaped washers 26 and 32 and the cup-shaped barriers 30 and 36 are made from insulating material; and they are made so they are fiexible and resilient. One insulating material which has been found to be very useful in making those washers and barriers is forming-fibre. The cup-shaped washers 26 and 32 and the -barriers 30' and 36 can be formed by simple pressing or punching operations.

The numeral 38 denotes an elongated, small-diameter, wire-like, fusible element; and one end of that fusible element is threaded through the opening 28 in the cupshaped washer 26 while the other end of that fusible element is threaded through the opening 34 in the cupshaped washer 32. The left-hand end of the fusible element 38 passes between the inner surface of the cupshaped washer 26 and the outer surface of the cup-shaped barrier 30, passes around the rim of that cup-shaped barrier, and then is bent inwardly into the frusto-conical space defined by that cup-shaped barrier. The right hand end of the fusible element 38 passes between the inner surface of the cup-shaped washer 32 and the outer surface of the cup-shaped barrier 36, passes around the rim of that cup-shaped barrier, and then is bent inwardly into the frusto-conical space defined by that cup-shaped barrier. The diameter of the fusible element 38 is so small that bends can readily be formed in that fusible element.

The numeral 40 denotes a ferrule-like, metal terminal which is telescoped over the left-hand end of the casing 20; and the free edge of that terminal is rolled or crimped into the annular groove 22. The numeral 44 denotes a second ferrule-like; metal terminal which is telescoped over the right-hand end of the casing 20; and the free edge of that second terminal is rolled or crimped into the annular groove 24. Solder 42 electrically bonds and physically connects the left-hand end of the fusible element 38 to the terminal 40; and solder 46 electrically bonds and physically connects the right-hand end of that fusible element to the terminal 44.

In assembling the electric fuse of FIG. 1, the left-hand end of the fusible element 38 is passed through the casing 20 and is then passed through the opening 28 in the closed end of the cup-shaped Washer 26. Thereafter, that cupshaped washer has the frusto-conical portion thereof forced into the left-hand end of that casing, and has the annular flange thereof pressed against the left-hand end of that casing. The cup-shaped barrier 30 is then pressed into the frusta-conical recess defined by the frusto-conical portion of the cup-shaped washer 26; and the outer surface of that cup-shaped barrier will bend the adjacent portion of the fusible element 38 so it intimately engages the inner surface of the cup-shaped washer 26 and so it assumes the configuration shown by FIG. 1. After the cup-shaped barrier 30 has bent the adjacent portion of the fusible element 38 into intimate engagement with the cup-shaped washer 26, any excess length of the left-hand end of that fusible element will be cutoff; and the remaining portion of the left-hand end will be bent into the recess defined by that cup-shaped barrier. A small quantity of solder 42 will be placed within the frusto-conical recess defined by the cup-shaped barrier 30; and then the terminal 40 will be telescoped over the left-hand end of the casing 20, and the free edge of that terminal will be rolled or crimped into the annular groove. Thereafter, the opening 34 in the cup-shaped washer 32 will be threaded over the right-hand end of the fusible element 38; and that cup-shaped washer will have the frustoconical portion thereof forced into the right-hand end of the casing 20 and will have the annular flange thereon disposed in abutting engagement with that right-hand end of that casing. The cup-shaped barrier 36 will then 4be pressed into the frusto-conical recess defined by the frusto-conical portion of the cup-shaped barrier 32 to force the adjacent portion of the fusible element 38 to assume the configuration shown by FIG. l. A light tension should be maintained on the fusible element 38, as the cup-shaped barrier 36 is pressed into the frusto-conical space defined by the frusto-conical portion of the cupshaped Washer 32, so that fusible element will assume a position which is coincident with the geometric axis of the casing 20. As the cup-shaped barrier 36 is pressed into intimate engagement with the inner surface of the cupshaped washer 32, any excess length of the right-hand end of the fusible element 38 will be cut off; and the remaining portion of that right-hand end will be bent inwardly over the rim of that cup-shaped barrier. Thereafter, a small quantity of solder 46 will be placed within the frustoconical recess defined by the cup-shaped barrier 36; and then the terminal 44 will be telescoped over the right-hand end of the casing 20, and the free edge of that terminal will be rolled or crimped nito the annular groove 24. The mechanically-assembled electric fuse Will then be set with its elongated axis vertical and with the terminal 40 resting upon a heated plate to cause the lump 42 of solder, located in the frusto-conical space between the inner surface of that terminal and the cup-shaped barrier 30, to melt. That molten solder will assume the configuration shown in FIG. l, and it will then be cooled to electrically bond and mechanically connect the left-hand end of the fusible element 38 to the terminal 40. At this time, the mechanically-assembled electric fuse Will be inverted and the terminal 44 will be set upon the heated plate, so the lump 46 of solder within the frusto-conical space defined by the inner surface of that terminal and the cupshaped barrier 36 will melt. That lump of solder will assume the configuration shown in FIGS. l and 2; and it will subsequently be permitted to cool to electrically bond and mechanically connect the right-hand end of the fusible element 38 to the terminal 44.

The electric fuse of FIG. 1 will carry its rated current continuously; and that rated current can be established with a highly-desirable degree of accuracy, because that fusible element will have a fixed position within the casing 20. Specically, that fusible element will be coincident with the geometric axis of that casing, and it will be held there by the closed ends of the cup-shaped Washers 26 and 32, As a result, all points on the major portion of the length of that fusible element will be spaced the same radial distance from all portions of the interior of the casing 20, and thus will have a uniform volume of air between them and that interior. Furthermore, the casing 20 will be devoid of arc-extinguishing filler material, and hence the fusible element 38 will not be contacted by arc-extinguishing filler material; and this means that the electric fuse of FIGS. 1 and 2 will not experience the variations in heat transference which are experienced by electric fuses that have small fusible elements that are surrounded by arc-extinguishing filler material. The overall result is that the electric fuse of FIGS. l and 2 can have a desirably-precise rating.

One embodiment of the electric fuse shown in FIG. l hasan overall length of one and one-half inches, has a diameter of thirteen thirty-seconds of an inch, and has a rating of four and one-half amperes or less; and that embodiment of electric fuse can be used to interrupt circuits having voltages as high as six hundred volts applied thereto. When the current flowing through such a circuit exceeds the rating of the electric fuse of FIGS. 1 and 2 by a predetermined value for a predetermined period of time, the central portion of the fusible element 38 will fuse. The resulting arc can burn back the two ends of the fusible element 38 until the resulting are plasma reaches the imperforate cup-shaped barriers 30 and 36.

Those imperforate cup-shaped barriers will isolate the terminals 40 and 44 from the arc plasma, and thus will keep the metal of those terminals from feeding the arc. The arc will not be able to consume the portions of the fusible element 38 which are disposed between the interior surfaces of the cup-shaped washers 26 and 32 and the exterior surfaces of the cup-shaped barriers 30 and 36; because those cup-shaped washers and those cupshaped barriers will absorb heat from the arc, and because that arc will be unable to follow the bends in that fusible element. As a result, the arc will quickly become extinguished; and the pressures within the casing 20v will be unable to rise to objectionably high levels.

The forming-fibre from which the cup-shaped washers 26 and 32 and the cup-shaped barriers 30 and 36 are made is relatively soft. As a result, the bending of they fusible element 38 by those cup-shaped washers and by those cup-Shaped barriers during the assembling of the electric fuse of FIGS. 1 and 2 will not subject that fusible element to hurtful stresses. This is important; because that fusible element 38 will be so small that it will be quite weak and must be protected against undue stresses.

FIG. 3 shows a second preferred embodiment of electric fuse that is made in accordance with the principles and teachings of the present invention; and that fuse has a casing 50 which can be identical to the casing 20 of FIG. l-having shallow annular grooves 52 and 54 which can be identical to the shallow annular grooves 22 and 24. Ferrule-like, metal terminals 62 and 64, which can be identical to the ferrule-like, metal terminals 40 and 44 of FIG. l, are telescoped over the opposite ends of the casing 50 and have the free edges thereof rolled or crimped into the annular grooves 52 and 54.

The numeral 60 denotes an elongated, small-diameter, wire-like fusible element; and one end of that fusible element is bent outwardly across the left-hand end of the casing 50 and then is bent into engagement with the outer surface of that casing. The other end of that fusible element is'bent outwardly across the right-hand end of that casing, and then is bent along the outer surface of that casing. A cup-shaped barrier 56 of frusto-conical form is pressed into the left-hand end of the casing 50 before the ferrule-like terminal 62 is telescoped over that end. The frusto-conical portion of that barrier will be forced into the left-hand end of that casing, but the annular flange of that cup-shaped barrier will abut the lefthand end of that casing. That annular flange will be engaged and held by the ferrule-like terminal 62; and that ferrule-like terminal will intimately engage the portion of the fusible element 60 which extends along the outer surface of the casing Silthereby making electrical contact with that portion. A similar cup-shaped barrier 58 will be pressed within the right-hand end of the casing 50l before the ferrule-like terminal 64 is telescoped over that end. The fmsto-conical portion of that barrier will be forced into the right-hand end of that casing, but the annular flange of that cup-shaped barrier will abut the right-hand end of that casing. That annular flange will be engaged and held by the ferrule-like terminal 64; and that ferrule-like terminal will intimately engage the portion of the fusible element 60 which extends along the outer surface of the casing Sil-thereby making electrical contact with that portion.

The ferrule-like terminals 62 and 64 would tend to force the outwardly-bent portions of the fusible element 60 into intimate engagement with the minute rough places, which inevitably exist at the ends of fuse casings, if the inner ends of those ferrule-like terminals engaged those outwardly-bent portions. However, the annular anges on the cup-shaped barriers 56 and 58 keep those inner ends of those ferrule-like terminals from engaging those outwardly-bent portions; and, in addition, they will yield to limit the forces which the inner ends of those ferrule-like terminals can apply to those outwardly-bent portions. As a result, those annular flanges protect the outwardly-bent portions of the fusible element 60 from injury.

The electric fuse of FIG. 3 will carry its rated current continuously; but it will respond to overloads of predetermined value and of predetermined duration to fuse. The arc which forms as that fusible element fuses can burn back the two ends of that fusible element until the resultlng arc plasma reaches the imperforate cup-shaped barriers 56 and 58. The arc will be cooled by the sides of those cup-shaped barriers and by the adjacent portions of the inner surface of the casing 50; and hence that arc will be quickly extinguished, and the pressure within the casing 50 -will be unable to rise to objectionably high levels.

Referring particularly to FIG. 4, the numeral 70 denotes a casing which can be identical to the casing 20 of FIGS. l and 2, the numeral 72 denotes a shallow annular groove which can be identical to the shallow annular groove 22, and the numeral 82 denotes a ferrule-like, metal terminal which can be identical to the ferrule-like, metal material 40. The numeral 74 denotes a disc-type washer which has a central opening 76 therein; and that washer is dimensioned so it can be forced into the casing 70. The left*hand end of an elongated, small-diameter, wire-like, fusible element 80 will be passed through the opening 76, and then will be bent outwardly by the closed end of a cup-shaped barrier 78. That cup-shaped barrier has a frusto-conical portion which can be pressed into the left-hand end of the casing 70 and has a closed end which closely abuts the left-hand face of the washer 74. An annular flange on that cup-shaped barrier abuts the left-hand end of the casing 70; and that annular ange will be held in engagement with that left-hand end of the ferrule-like terminal 82. The left-hand end of the fusible element 80 will pass outwardly across the outer end of the casing 70 and then will be bent along the outer surface of that -casing; and it will be clamped in position by, and will make electrical engagement with, the ferrule-like terminal 82. The right-hand end of the electric fuse of FIG. 4 can be a mirror-image of the left-hand end of that fuse.

Referring particularly to FIG. 5, the numeral denotes a casing which can be identical to the casing 20 of FIGS. 1 and 2, the numeral 92 denotes a shallow annular groove which can be identical to the shallow annular groove 22, and the numeral 102 denotes a ferrule-like, metal terminal which can be identical to the ferrule-like, metal terminal 40. The numeral 94 denotes a washer of insulating material which has a central opening 96 therein; and that washer can be identical to the washer 74 in FIG. 4. The numeral 98 denotes a disc-like barrier which has a diameter larger than the inner diameter of the casing 90 but smaller than the inner diameter of the ferrule-like terminal 102. The numeral 100 denotes an elongated, small-diameter, wire-like, fusible element which has the left-hand end thereof extending through the opening 96 in the washer94 and then bent outwardly between that washer and the disc-like barrier 98. That end of that fusible element passes along the left-hand end of the casing 90 and then is bent forwardly along the outer surface of that casing; and that end of that fusible element is held in position, and is electrically engaged Iby the terminal 102. The right-hand end of the electric fuse of FIG. 5 can be a mirror-image of the left-hand end of that fuse.

The electrical fuses of FIGS. 4 and l resemble the electric fuses of FIGS. 1 and 2 in that they employ washers with centrally-located openings to hold the fusible elements thereof coincident with the geometric axes of the casings thereof. The electric fuses of FIGS. 4 and 5 resemble the electric fuse of FIG. 3 in that they rely upon the resilience of the insulating material of the imperforate barrier thereof to cushion the outwardly-bent end portions of the fusible elemen-ts thereof.

The annular grooves, in the exteriors of the casings of the electric fuses shown in the drawing, are necessary where those casings are made of substantially-unyielding material such as glass melamine. However, where those casings are made from yieldable material such as bre, those annular grooves are not needed; and the free edges of the ferrule-like, metal terminals of the electric fuses can be rolled or crimped directly into the exteriors of those casings.

In some instances it is desirable to pass the ends of the fusible element through openings in the closed ends of the ferrule-like, metal terminals of an electric fuse and then solder those ends of that fusible element to the outer faces of those closed ends of those terminals. In those instances, the ends of the fusible elements shown in the drawing will be bent around the imperforate barriers of insulating material, will be directed inwardly toward the geometric axes of the casings `of the electric fuses, and then will be bent into alignment with those geometric axes to pass through the openings in the closed ends of the ferrule-like, metal terminals.

The barriers of insulating material shown in the drawing will, where they are made of libre, evolve arc-extinguishing gases when an arc develops. If desired, those barriers of insulating material could lbe made of paper, cloth, asbestos or the like which has been impregnated with de-ionizing material, so those barriers will evolve deionizing vapors and gases when an arc develops.

Whereas the drawing and accompanying description have shown and described several preferred embodiments of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

What I claim is:

1. An electric fuse which comprises:

a casing,

terminals permanently secured to said casing,

a barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of one of said terminals,

a second barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of the other of said terminals,

an elongated, fusible element that is disposed within said casing and that is electrically connected to sald terminals,

said fusible element having a total overall length greater than the length of said casing,

said fusible element having a fixed position within said casing, wherein the major portion of the length thereof is spaced inwardly of and out of engagement with said casing and wherein said major portlon of the length thereof is engaged only by air, U

said fixed position of said fusible element wlthrn said casing enabling said fusible element to have a predlctable rate of radiation of heat to said casing,

said barriers of insulating material being imperforate to said fusible element and being interposed between said inner surfaces of said terminals and said major portion of the length of said fusible element, and said fusible element being bent to reach said inner Surfaces of said terminals,

the bends in said fusible element being immediately adjacent said barriers of insulating material and being cushioned by said barriers of insulating material,

said barriers of insulated material and said bends in in said fusible element coacting to keep any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short.

2. An electric fuse which comprises:

a casing,

terminals permanently secured to said casing,

a barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of one of said terminals,

a second barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of the other of said terminals,

an elongated, fusible element that is disposed within said casing and that is electrically connected to said terminals,

said fusible element having a total overall length greater than the length of said casing,

said fusible element having a fixed position within said casing, wherein the major portion of the length thereof is spaced inwardly of and out of engagement with said casing and wherein said major portion of the length thereof is engaged only by air,

said fixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material being imperforate to said fusible element and being interposed between said inner surfaces of said terminals and said major portion of the length of said fusible element, and said fusible element being bent to reach said inner surfaces of said terminals,

the bends in said fusible element being immediately adjacent said barriers of insulating material and being cushioned by said barriers of insulating material,

said barriers of insulating material and said bends in said fusible element coacting to keep any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short,

the ends of said fusible element being bent around the edges of said barriers of insulating material and being disposed between said inner surfaces of said terminals and those surfaces of said barriers of insulating material which confront said inner surfaces of said terminals.

3. An electric fuse which comprises:

a casing,

terminals permanently secured to said casing,

a barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of one of said terminals,

a second barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of the other of said terminals,

an elongated, fusible element that is disposed within said casing and that is electrically connected to said terminals,

said fusible element having a total overall length greater than the length of said casing,

said fusible element having a fixed position within said casing, wherein the major portion of the length thereof is spaced inwardly of and out of engagement with said casing and wherein said major portion of the length thereof is engaged only by air,

said fixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material being imperforate to said fusible element and being interposed between said inner surfaces of said terminals and said major portion of the length of said fusible element, and said fusible element being bent to reach said inner surfaces of said terminals,

the bends in said fusible element being immediately adjacent said barriers of insulating material and being cushioned by said barriers of insulating material,

said barriers of insulating material and said bends in said fusible element coacting to keep any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short.

the ends of said fusible element being bent around the ends of said casing, and

portions of said barriers of insulating material being disposed between said ends of said fusible elements and said inner surfaces of said terminals to cushion the forces which said terminals apply to said ends of said fusible element.

4. An electric fuse which comprises:

a casing,

terminals permanently secured to said casing,

a barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of one of said terminals,

a second barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of the other of said terminals,

an elongated, fusible element that is disposed within said casing and that is electrically connected to said terminals,

said fusible element having a total overall length greater than the length of said casing,

said fusible element having a fixed position within said casing, wherein the major portion of the length thereof is spaced inwardly of and out of engagement with said casing and wherein said major portion of the length thereof is engaged only by air,

said fixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material being imperforate to said fusible element and being interposed between said inner surfaces of said terminals and said major portion of the length of said fusible element, and said fusible element being bent to reach said inner surfaces of said terminals,

the bends in said fusible element being immediately adjacent said barriers of insulating material and being cushioned by said barriers of insulating material,

said barriers of insulating material and said bends in said fusible element coacting to keep any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short,

said -barriers of insulating material being cupshaped,

the cup-like portions of said barriers of insulating material extending inwardly of the ends of said casing, and

annular flanges on said barriers of insulating material which extend outwardly of said cup-like portions of said barriers of insulating material to abut the end faces of said casing.

5. An electric fuse which comprises:

a casing,

terminals permanently secured to said casing,

a barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of one of said terminals,

a second barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of the other of said terminals,

, an elongated, fusible element that is disposed within said casing and that is electrically connected to said terminals,

said fusible element having a total overall length greater than the length of said casing,

said fusible element having a fixed position Within said casing, wherein the major portion of the length thereof is spaced inwardly of and out of engagement with said casing and wherein said major portion of the length is engaged only by air,

, said fixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material being imperforate to said fusible element and being interposed between said inner surfaces of said terminals and said major portion of the length of said fusible element, and said fusible element being bent to reach said inner surfaces of said terminals,

the bends in said fusible element being immediately adjacent said barriers of insulating material and being cushioned by said barriers of insulating material,

said barriers of insulating material and said bends in said fusible element coacting to keep any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short,

washers of insulating material disposed inwardly of said barriers of insulating material, and

the ends of said fusible element extending through the openings in said washers of insulating material but not extending through said barriers of insulating material.

6. An electric fuse which comprises:

a casing,

terminals permanently secured to said casing,

a barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of one of Said terminals,

a second barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of the other of said terminals,

an elongated, fusible element that is disposed within said casing and that is electrically connected to said terminals,

said fusible element having a total overall length greater than the length of said casing,

said fusible element having a xed position within said casing, wherein the major portion of the length thereof is spaced inwardly of and out of engagement with said casing and wherein said major portion of the length thereof is engaged only by air,

said iixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material being imperforate to said fusible element and being interposed between said inner surfaces of said terminals and said major portion of the length of said fusible element, and said fusible element being bent to reach said inner surfaces of said terminals,

the bends in said fusible element being immediately adjacent said barriers of insulating material and b eilng cushioned by said barriers of insulating mater1a said barriers of insulating material and said bends in said fusible element coacting to keep any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short,

washers of insulating material disposed inwardly of said barriers of insulating material, and

said washers having openings therein that are spaced inwardly of the inner surface of said casing and that hold the fusible portion of said fusible element spaced inwardly from the inner surface of said casing.

7. An electric fuse which comprises:

a casing,

terminals permanently secured to said casing,

a barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of one of said terminals,

. a second barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of the other of said terminals,

an elongated, fusible element that is disposed within said casing and that is electrically connected to said terminals,

said fusible element having a total overall length greater than the length of said casing,

said fusible element having a fixed position within said casing, wherein the major portion of the length thereof is spaced inwardly of and out of engagement with said casing and wherein said major portion of the length is engaged only by air,

said fixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material being imperforate to said fusible element and being interposed between said inner surfaces of said terminals and said major portion of the length of said fusible element, and said fusible element being bent to reach said inner surfaces of said terminals,

the bends in said fusible element being immediately adjacent said barriers of insulating material and being cushioned by said barriers of insulating material,

said barriers of insulating material and said bends in said fusible element coacting to keep any arc, which may ldevelop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short,

washers of insulating material disposed inwardly of said barriers of insulating material,

the ends of said fusible element extending through openings in said washers of insulating material which are adjacent the geometric axis of said casing, Iand said openings in said washers of insulating material holding the fusible portion of said fusible element adjacent the geometric axis of said casing.

8. An electric fuse which comprises:

a casing,

terminals permanently secured to said casing,

a barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of one of said terminals,

a second barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of the other of said terminals,

an elongated, fusible element that is disclosed within said casing and that is electrically connected to said terminals,

said fusible element having a total overall length greater than the length of said casing,

said fusible element having a fixed position within said casing, wherein the major portion of the length thereof is spaced inwardly of and out of engagement with said casing and wherein said major portion of the length thereof is engaged only by air,

said fixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material being imperforate to said fusible element and being interposed between said inner surfaces of said terminals and said major portion of the length of said fusible element, and said fusible element being bent to reach said inner surfaces of said terminals,

the bends in said fusible element being immediately adjacent said barriers of insulating material and being cushioned by said barriers of insulating material,

said barriers of insulating material and said bends in said fusible element coacting to keep any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short,

washers of insulating material disposed inwardly of said barriers of insulating material,

said barriers of insulating material being cup-shaped,

said washers of insulating material being cup-shaped,

and the cup-like portions of said washers of insulating material and the cup-like portions of said barriers of insulating material extending inwardly of the ends of said casing.

9. An electric fuse which comprises:

a casing,

terminals on said casing,

a barrier of insulating material disposed within said casing adjacent the inner surface of one of said Iterminals,

a second barrier of insulating material disposed within said casing adjacent the inner surface of the other of said terminals,

a fusible element that is disposed within said casing and that is electrically connected to said terminals, said fusible element having a fixed position within said casing,

said fixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material keeping any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short,

Washers of insulating material disposed inwardly of said barriers of insulating material,

said washers of insulating material being cup-shaped,

said barriers of insulating material being cup-shaped,

and

the cup-like portions of said barriers of insulating material extending into the cup-like portions of said washers of insulating material.

10. An electric fuse which comprises:

a casing,

terminals permanently secured to said casing,

a barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of one of said terminals,

a second barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of the other of said terminals,

an elongated, fusible element that is disposed within said casing and that is electrically connected to said terminals,

said fusible element having a total overall length greater than the length of said casing,

said fusible element having a fixed position within said casing, wherein the major portion of the length thereof is spaced inwardly of and out of engagement with said casing and wherein said major portion of the length thereof is engaged only by air,

said fixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material being imperforate to said fusible element and being interposed between said inner surfaces of said terminals and said major portion of the length of said fusible element, and said fusible element being bent to reach said inner surface of said terminals, p

the bends in said fusible element being immediately adjacent said barriers of insulating material and being cushioned by said barriers of insulating material,

said barriers of insulating material and said bends in said fusible element coacting to keep any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short,`

washers of insulating material disposed inwardly of said barriers of insulating material, and

the ends of said fusible element being bent outwardly relative to the geometric axis of said casing and extending between confronting surfaces of said Washers of insulating material and of said barriers of insulating material until they reach said casing.

11. An electric fuse which comprises:

a casing,

terminals on said casing,

a barrier of insulating material disposed within said casing adjacent the inner surface of one of said terminals,

a second barrier of insulating material disposed within said casing adjacent the inner surface of the other of said terminals,

a fusible element that is disposed within said casing and that is electrically connected to said terminals,

said fusible element having a fixed position within said casing,

said fixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material keeping any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short,

washers of insulating material disposed inwardly of said barriers of insulating material, and

the ends of said fusible element being bent outwardly relative to the geometric axis of said casing and extending between confronting surfaces of said washers of insulating material and of said barriers of insulating material until they reach said casing,

said barriers of insulating material and said washers of insulating material being cup-shaped to provide a plurality of bends in each end of said fusible element.

12. An electric fuse which comprises:

a casing,

terminals permanently secured to said casing,

a barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of one of said terminals,

a second barrier of insulating material disposed within said casing adjacent, but disposed inwardly of, the inner surface of the other of said terminals,

an elongated, fusible element that is disposed within said casing and that is electrically connected to said terminals,

said fusible element having a total overall length greater than the length of said casing,

said fusible element having a fixed position within said casing, wherein the major portion of the length thereof is spaced inwardly of and out of engagement with said casing and wherein said major portion of the length thereof is engaged only by air,

said fixed position of said fusible element within said casing enabling said fusible element to have a predictable rate of radiation of heat to said casing,

said barriers of insulating material being imperforate to said fusible element and being interposed between said inner surfaces of said terminals and said major portion of the length of said fusible element, and said fusible element being bent to reach said inner surfaces 0f said terminals,

the bends in said fusible element being immediately adjacent said barriers of insulating material and being cushioned by said barriers of insulating material,

said barriers of insulating material and said bends in said fusible element coacting to keep any arc, which may develop as said fusible element fuses, from extending to and being fed by said terminals,

whereby said casing can be relatively short,

washers of insulating material disposed inwardly of said barriers of insulating material, and

said washers of insulating material being cup-shaped,

the closed ends of said cup-shaped washers having centrally-located openings therein to accommodate the ends of said fusible element and to thereby hold the fusible portion of said fusible element adjacent the geometric axis of said casing.

References Cited UNITED STATES PATENTS 745,969 12/1903 McCarthy 337-248 1,252,141 12/1916 Murray 337-246 1,450,670 4/ 1923 La Mar 337-241 2,172,226 9/1939 Smith 337-248 2,713,098 7/1955 Swain 337-246 FOREIGN PATENTS 340, 865 9/ 1921 Germany.

BERNARD A. GILHEANY, Primary Examiner H. B. GILSON, Assistant Examiner U.S. C1. X.R. 33 7-246 

